Membrane cells are used in chemical analysis to partition a sample contained on one side of a membrane from a compartment positioned on the other side of the membrane The sample contains a component of interest that permeates across the membrane into the compartment. The contents of the compartment can then be analyzed for the component of interest. If the sample contains another component that does not permeate across the membrane which otherwise would interfere with the analysis of the component of interest, then the use of a membrane cell in the analysis of the component of interest is beneficial.
Membrane cells can incorporate sheet type membranes and tubular type membranes. A cell using a sheet type membrane can be made by clamping the membrane between two blocks, each block having a cavity machined into it exposed to the membrane, the cavities being juxtaposed across the membrane so that a sample can be placed in one of the cavities with the contents of the other cavity being analyzed for the component of interest that has permeated across the membrane. A cell using a tubular membrane can be made by sealing the ends of a tubular membrane inside and to the ends of a metal tube leaving an annular space between the central portion of the inside of the metal tube and the central portion of the outside of the tubular membrane so that a sample can be placed in the annular space with the contents of the bore of the membrane being analyzed, or conversely, the sample can be placed in the bore of the tubular membrane with the contents of the annular space being analyzed.
One important application of membranes in chemical analysis is in the field of mass spectrometry. The membrane of a membrane cell is used to partition a sample from the vacuum inlet of a mass spectrometer. A component of interest of the sample permeates across the membrane, evaporates into the vacuum on the other side of the membrane and is carried into the mass spectrometer for analysis Usually, a valve is placed in the vacuum line between the membrane cell and the mass spectrometer so that passage of the component of interest into the mass spectrometer can be stopped if desired. Frequently, several membrane cells are connected to a mass spectrometer through such valves so that each can be respectively analyzed in turn. It would be an advance in this art if the valve and the membrane cell could be combined into one unit to reduce the number of apparatus components needed.